Optical discs such as digital versatile discs (DVDs) or Blu-ray (a registered trademark) discs (BD) have been widely used as media for recording various data in addition to images and programs.
The optical discs such as BDs are required to perform high-density information recording.
As a method of increasing the density of optical discs, there are a method of reducing a channel bit length, that is, a mark length, and increasing a density in a linear density direction and a method of narrowing a track pitch.
However, in a case where the density is increased in the linear density direction, there arises a problem that inter-symbol interference increases.
Further, if the track pitch is narrowed, information leaking from an adjacent track (an adjacent track crosstalk) increases.
In order to reduce the adjacent track crosstalk (hereinafter referred to simply as a “crosstalk”), various methods have been proposed.
For example, Patent Document 1 (International Publication No. WO 2016/006157) discloses a configuration of generating a reproduction signal in which the crosstalk is reduced by dividing a light receiving region of a photo detector and performing an adaptive equalization process using a plurality of light receiving signals obtained from respective split regions.
However, in this method, it is difficult to reliably analyze a recording signal of an adjacent track, and it is difficult to remove the crosstalk sufficiently.
Further, a technique of cancelling the crosstalk by supplying a reproduction signal of a track of a reproduction target and reproduction signals of tracks on both sides thereof to an adaptive equalizer unit and controlling a tap coefficient of the adaptive equalizer unit is disclosed in Patent Document 2 (Japanese Patent Application Laid-Open No. 2015-05775.3), Patent Document 3 (Japanese Patent Application Laid-Open No. 2012-079385), Patent Document 4 (Japanese Patent Application No. 4184585), and the like.
However, in the configuration described in Patent Documents mentioned above, in order to acquire a signal from which the crosstalk signal has been removed from a read signal of a current reproduction track, it is necessary to adjust, phases of the read signal of the current reproduction track and the read signals of the tracks on both sides thereof and then input the resulting signal to the adaptive equalizer unit.
For this process, a memory for temporarily storing the read signal of the track adjacent to the current reproduction track or a delay processing configuration is required, and thus the required memory capacity increases, and there is a problem in that the circuit size increases.